Bath treatment of Atlantic salmon (Salmo salar) with amoebae antigens fails to affect survival to subsequent amoebic gill disease (AGD) challenge

There is no consistent evidence of resistance of Atlantic salmon (Salmo salar) to amoebic gill disease (AGD), despite either a prior history of AGD, passive immunisation or active immunisation. Here, fish were bathed in amoebae antigens from either an avirulent in vitro cultured strain or wild-type Neoparamoeba pemaquidensis and challenged with gill-derived amoebae 27 days post-treatment. Neither bath treatment enhanced survival compared to a placebo treated group of fish. Similarly treatment did not influence the proportion of AGD-affected gill filaments in fish surviving the AGD challenge. It is not known if the failure of the treatments to elicit protection was mediated by a lack of an immune response or if an immune response was ineffective during the AGD challenge.